Final answer:
The process most affected by blocking actin function during cell division is cytokinesis, where actin microfilaments are essential for forming the cleavage furrow to divide the cell into two.
Step-by-step explanation:
If actin function was blocked, the process of cell division that would be most affected is cytokinesis. During cytokinesis, actin microfilaments interact with myosin to form a cleavage furrow that constricts the cell into two daughter cells. Actin filaments also play a role in providing structural support to intestinal microvilli and enabling their movement independent of peristalsis. While microfilaments are crucial for cytokinesis, microtubules, composed of α- and β-tubulin, are responsible for segregating chromosomes during earlier stages of mitosis, such as prophase, metaphase, and anaphase, by forming the mitotic spindle.